The present invention relates to an analyzing method using X-ray reflectance measurement, more specifically to an element concentration measuring method and apparatus for measuring concentrations of elements adhered on a surface of a sample-to-be-measured and/or segregated on an interface of films, and a method and apparatus for fabricating a semiconductor device.
With the recent larger scale and higher integration of semiconductor devices, insulation films, metal films, dielectric films, magnetic films, etc. have been further thinned. What significant here is how to control composite elements segregated on surfaces of samples or interfaces of multi-layer films.
For example, in a semiconductor device including a MOS transistor, to control diffusion of boron (B) in the silicon substrate and obtain low interface state it is often conducted that the gate insulation film of silicon oxide film is formed and then heat-treated in an N.sub.2 O or an NO atmosphere to introduce nitrogen into the interface between the silicon substrate and the gate insulation film. Toproduce sufficient effect it is necessary to accurately quantify a concentration of nitrogen to be introduced.
Impurities, such as boron, phosphorus (P), antimony (Sb), arsenic (As), are segregated In high concentrations between the silicon substrates and the gate insulation films may affect electric characteristics of the semiconductor devices. It is also important to control segregation quantities of such segregated impurities.
It is very effective to quantify impurities adhered and segregated on surfaces of samples as well as interfaces of the samples so as to improve device characteristics and inline process control.
In measuring elements adhered or segregated on such interfaces and surfaces SIMS (Secondary Ion Mass Spectroscopy) is dominantly used. SIMS is a method for quantifying concentrations of traces of elements contained in a sample by irradiating primary ions to the sample to sputter the surface of the sample and mass-analyzing secondary ions in the sputtered particles.
SIMS is a measuring means which enables the measurement with high sensitivity but destructively measures a depth-wide impurity concentration distribution by sputtering the surface of a sample. It is difficult to uniformly sputter a sample surface so that measured impurity profiles cannot be abruptly changed at the interfaces. Accordingly SIMS is not usable in line process control, to which non-destructive inspection is essential. It is impossible for SIMS to quantify impurity concentrations in a very thin region. The SIMS measurement costs much.
Measuring techniques other than SIMS are AES (Auger Electron Spectroscopy, XPS (X-ray Photoelectron Spectroscopy), fluorescence analysis, ellipsometry, etc. are known.
In AES and XPS, profiles cannot be also abruptly changed at the interface regions due to the sputtering as well as SIMS and escape lengths (about 1 nm) of measured electrons. AES and XPS have so low sensitivity that lower quantizable concentration limits are several percentages, and are not suitable to quantify elements segregated in interfaces. The measurement must be conducted in vacuum, which is unsuitable for composition control of thin films.
Fluorescence analysis, in which fluorescent X-rays radiated when X-rays are irradiated to a sample are measured to give amounts of content elements, based on intensities of the fluorescent X-rays, can measure a total amount of fluorescent elements but cannot measure a distribution of the elements in the sample, which makes it difficult to evaluate concentrations of elements on a surface or an interface. In measuring nitrogen in an oxide film, it is difficult to separate nitrogen from oxygen, based on fluorescent X-rays.
Ellipsometry, which is an optical method and can make a non-destructive inspection, has a possibility that a concentration will be quantified based on reflective index changes of a film due to segregated elements. However, the ellipsometry cannot measure a concentration distribution, as cannot the fluorescence analysis, and it is difficult to evaluate element concentrations in a surface or an interface.
As described above, none of the conventional element concentration measuring methods are sufficient for quantifying a concentration of an element segregated on a surface and an interface. An element concentration measuring method which can measure with good precision readily in line a concentration of an element segregated on a surface and an interface.